In concrete batching and asphalt plant automation, the PLC is the bridge between the field and the control room. The PLC drives gates, motors and pumps; weighing, recipes and reporting are usually done by the automation software on the PC. How these two talk to each other directly determines how flexible the plant is. This page explains Modbus TCP and why it is a good choice for plant automation.
What is Modbus TCP?
Modbus is an open, simple communication protocol that has been used in industry for a long time. Modbus TCP is the version that runs over Ethernet. The PC (client) reads or writes values at specific addresses in the PLC (server):
- Coils: single-bit outputs, such as starting a motor or opening a gate.
- Discrete inputs: single-bit inputs, such as a thermal fault, a gate-open sensor or an empty-bin signal.
- Registers: numeric values, such as scale weights, temperatures and frequency references.
Why Modbus TCP?
- Open standard: not tied to a brand. PLCs from many manufacturers — Delta, Siemens, Schneider, Mitsubishi, Omron and others — support Modbus TCP natively or with a module.
- Standard Ethernet: no special cable or card; the control room PC connects to the PLC with a network cable.
- Easy maintenance: which data sits at which address is defined in a table. Addresses can be read and written one by one when troubleshooting.
IO map: keep addresses out of the code
A common mistake in plant automation is writing PLC addresses into the program. When equipment is added or the PLC changes, the program has to be rebuilt. The right approach is to define every input/output and its address in a separate configuration file — the IO map. For a new plant, the file changes, not the software.
Network layout and security
- Use fixed IP addresses between the PLC and the control PC.
- Do not mix the automation network directly with the office network and the internet; if remote support is needed, plan a controlled path.
- If the connection drops, the software must show it immediately, and a safe state should be defined on the PLC side so outputs do not stay uncontrolled.
Which PLCs does DKT software work with?
DKT CPlants and DKT APlants talk to the PLC over Modbus TCP and are designed to work with PLCs that support Modbus TCP. In the field they run on plants with Delta DVP-SE and Delta AS228R. All connections are defined in the IO map file; for a different PLC brand, send us the IO list and PLC model and we will work out addressing and compatibility together.
Frequently asked questions
Can Modbus TCP be used with a Siemens PLC?
Yes. Series such as Siemens S7-1200 and S7-1500 can be configured as a Modbus TCP server. Addressing is defined in the PLC program and the automation software reads these addresses from the IO map.
What is the difference between Modbus TCP and Modbus RTU?
Modbus RTU runs over a serial line (such as RS-485), Modbus TCP over Ethernet. Using Ethernet between the control PC and the PLC makes installation and troubleshooting easier.
Does the PLC program change when the automation software is replaced?
In most cases the PLC’s field logic stays; only the addresses the software reads and writes are made accessible over Modbus TCP.
What happens if the connection between the PLC and the PC drops?
The software should show the loss of connection immediately, and the PLC should be configured to put outputs into a safe state when communication is lost.
Related pages
- Plant automation retrofit
- Concrete batching plant software (DKT CPlants)
- Asphalt plant control software (DKT APlants)
- Asphalt plant weighing system
Send us your IO list
The plant’s input/output list and PLC model are enough. DKT APlants for asphalt plants, DKT CPlants for concrete batching plants — we check compatibility together. WhatsApp: +90 547 909 99 90